1. Field of the Invention
The present invention relates generally to a setting method for blasting in a bar-like charge for blasting ground or rock employing an explosive. More specifically, the invention relates to a setting method for blasting in a bar-like charge system having a predetermined blast hole angle .alpha., a predetermined blast hole length M, a predetermined blast hole diameter d, a charge length N and a filler length P with respect to a free surface GL of said ground or the rock, instead of a single point concentrated charge system.
2. Description of the Related Art
Conventionally, land cultivation has been normally performed for undeveloped moor and forest and so forth, it has not caused serious problems by merely considering efficiency of blasting with paying attention for avoidance of accident associated with blasting, such as damaging by flying rock and so forth.
However, in the recent years, due to increasing of population on the earth, it is increasing a chance to perform blasting in the area close to the human resident area or in the city. Associating with this, the conventional blasting method merely seeking for efficiency of blasting should cause damaging of the human body and of other constructions, such as neighbourhood houses, buildings and so forth by flying rock and so forth, inherently.
For assuring security with avoiding flying rock accident, it is given importance for reducing amount of an explosive. However, when amount of the explosive is reduced absurdly, efficiency of blasting is inherently lowered unacceptably to border progree of constructional work. Accordingly, it is desired to use the maximum amount of explosive in a range where flying rock will not be caused in the free surface to achieve both of the security and efficiency, in blasting operation.
In such circumstance, as a method for setting blasting in consideration of both of security and efficiency, Hauser's equation has been known. Hauser's equation is directed to a single point concentrated charging and establishes the following equation for achieving both of the security and efficiency: EQU L=c.times.W.sup.3 ( 10)
wherein c is a blasting coefficient in a range of 0.25 to 0.45 and W is the least resistance length.
Studying the Houser's equation, assuming that the breaking radius D on the free surface is equal to the least resistance length W, i.e. when W=D, the volume of the rock to be broken by the explosive is in a reversed cone shaped configuration, from a volume of cone, the volume Vb of the rock to be broken into the reversed cone shaped configuration is expressed by: EQU Vb=W.sup.3
Accordingly, the foregoing equation (10) can be modified as: EQU L=c.times.Vb (10a)
The relational expression of L=c.times.Vb means that, in order to make the value of L within the safe range, the charge amount L is to be determined at a value to be safe within a range of blasting coefficient c=0.25 to 0.45 of the fracture volume Vb of the rock to be broken at the charge amount.
However, the Houser equation is directed to the single point concentrated charge system. Namely, without considering the volume of the charge amount as solid, the system considers that volume is charged at a single point concentrate manner.
In the practical blasting operation, the bar-like charge system is taken to charge the explosive within a pit or hole having a certain length H and a diameter d. Therefore, the explosive is present as a solid having a certain length (charge length (H-W) and the diameter d, wherein W is the least resistance length.
Accordingly, when the charge amount L required for blasting in the bar-like charging is derived employing the Houser's equation, a value far different from practical amount may be derived to cause significant danger. For example, when blasting of the rock is to be performed employing a dynamite having a diameter of explosive of 25 mm charged in a hole diameter d=25 mm, the charge amount L derived by the Houser's equation becomes: EQU L=cW.sup.3 =0.25.times.2.sup.3 =2 (kg)
assuming the blasting coefficient c=0.25 and the least resistance length W=2 m. This charge amount corresponds to a twenty of dynamites having explosive diameter of 25 mm, explosive length of 165 mm and weight of 100 g. When, these dynamites are charged in the 2 m of charge hole, the hole will be filled with 12.5 in number of the dynamites. Therefore, 7.5 in charge of dynamites cannot be charged in the charge hole. Therefore, in order to maintain the calculated charge amount, the diameter of the charging hole should be made greater to be 80 to 100, or more. However, the hole diameter d cannot be derived through the Houser's equation.
In the blasting operation in the bar-like charge, in practice, the modified Houser's equation L=cW.sup.3 is employed. Namely, with replacing W.sup.3 with DWH, the Houser's equation can be re-written as: EQU L=cDWH (11)
wherein
c: blasting coefficient; PA0 D: fracture radius in the free plain; PA0 W: least resistance length; and PA0 H: is a charge hole length
Here, it is quite dangerous to set the fracture radius D and the least resistance length W without establishing balance, in view of security. Therefore, it is required to establish a relationship where EQU W=D or W.apprch.D (12)
is satisfied.
However, even when the foregoing equations (11) and (12) are employed, it is still irrelative to the charge hole diameter d. Therefore, it is not possible to accurately determined the charge hole diameter d in relation to other element.
In this respect to this, the charge hole diameter d is typically experimentarily taught to be at 1/45 of the least resistance length W (see R. Gusteferson: "New Blasting Technology", Morikita Shuppan K. K., Apr. 10, 1981, Page 60). Also, Japan Industrial Explosive Association utilizes similar standard but widening allowable range to provide a guideline "In case of typical blasting, the least resistance length is within a range of 30 times to 60 times of the charge hole diameter". In other words, "the charge hole diameter d is 1/30 to 1/60 of the least resistance length" (see Ground Emission Division of Ministry of International Trade and Industry of Japan, "Explosive Safety Text Series 17", January, 1991, Page 24). In concrete example of this relationship, when the charge hole diameter is set at 3 cm, the least resistance length W can be within a range of 90 cm to 180 cm. Such range is too wide in view of criticalness of the least resistance length for possibility of occurrence of accident on the human being, and thus is dangerous.
The reason is that the least resistance length W in the blasting operation is a value representative of the shortest distance to the upper end of the explosive to the surface of the earth. When the value of the least resistance length is too short, accident due to flying rock may be caused. On the other hand, when the value of least resistance length is too long, fracture at the surface of the earth becomes insufficient to lower efficiency of operation. Therefore, as can be appreciated, the least resistance length W is quite important factor in determining the safety and efficiency in the blasting operation.
Here, a number of accident by blasts for construction works in Japan from 1979 to 1989 are counted 261, in which accident by flying rock are counted 160 cases, which are 61.3%.